A thermal imaging camera for spatially-resolved temperature measurement uses a thermally sensitive sensor array, in which a characteristic thermal radiation of an object is imaged onto an array of thermally sensitive sensor elements by a lens transmitting infrared radiation. For example, long-wave infrared radiation (LWIR) includes wavelengths in the range of approximately 8 to 14 μm. Due to the infrared radiation, the sensor elements warm up by amounts on the order of a few mK. An uncooled sensor array for characteristic thermal radiation may be realized cost-effectively on the basis of thermally sensitive diodes of silicon p-n junctions. The heating of the sensor element caused by the infrared radiation leads to a change in the current-voltage characteristic of a sensor element, which is able to be evaluated by electronics that are as low-noise as possible.
For the practical applicability of such a sensor element, it is necessary to honor further boundary conditions. In order to minimize an unwanted heat transfer from the sensor element, for example, the sensor element may be exposed micromechanically. In this manner, heating of the sensor element may be increased, and therefore the signal may be increased, so that a high signal-to-noise ratio may be attained. The thermal resolution of the sensor may thereby be improved. Furthermore, the individual sensor elements must have a greater extension than the wavelength used of approximately 8 μm; surface areas of approximately 12 μm2 are customary. In addition, each sensor element should have its own absorption layer in order to ensure the best possible absorption of the infrared radiation to be received. For example, silicon dioxide may be used for that purpose. In addition, the aim should be for sufficient mechanical stability of the sensor element with respect to vibrations. The observance of these boundary conditions is essential in constructing a low-noise sensor element for the photosensor of a thermal imaging camera, so that customary methods for improving a signal-to-noise ratio of the sensor element may not be usable.
An object of the present invention is to indicate a thermal diode for a photosensor of a thermal imaging camera, the thermal diode exhibiting the lowest noise possible. A further object of the invention is to indicate a corresponding photosensor. The invention achieves these objectives by a thermal diode and a photosensor having the features set forth in the description herein. The further descriptions herein describe more specific embodiments.